This invention relates generally to spinal fixation devices and more specifically relates to a system and associated method for minimally invasive installation of pedicle screws and spinal rods of spinal fixation constructs.
The human spinal column is a highly complex system of bones and connected tissues that provide support for the body and protects the delicate spinal cord and nerves. The spinal column includes a series of vertebrae stacked one atop the other. Each vertebral body includes a relatively strong cortical bone portion forming the outside surface of the body and a relatively weak cancellous bone portion forming the center of the body. An inter-vertebral disc is situated between each vertebral body that provides for cushioning and dampening of compressive forces applied to the spinal column. The vertebral canal containing delicate spinal cords and nerves is located just posterior to the vertebral bodies.
A variety of types of spinal column disorders may be caused by abnormalities, disease, trauma or the like and result in debilitating pain as well as diminished nerve function in many cases. One known technique to address many such spinal conditions is commonly referred to as spinal fixation. Surgical implants are used for fusing together and/or mechanically immobilizing adjacent vertebrae of the spine. Spinal fixation may also be used to improve the position of the adjacent vertebrae relative to one another so as to alter the overall alignment of the spine. Such techniques have been used effectively to treat many spinal conditions and to relieve pain suffered by the patient.
One particular spinal fixation technique includes immobilizing the spine by using orthopedic spine rods which run generally parallel to the spine. Exposing the spine posterially and fastening hooks or bone screws to the pedicles of the appropriate vertebrae accomplish this. The pedicle anchors or screws are generally placed two per vertebrae, one at each pedicle on either side of the spinal column and serve as anchor points for the spine rods. The aligning influence of the rods forces the spine to conform to a more desirable shape. In many cases, the spine rods are bent to achieve the desired curvature of the spinal column.
Installation of such spinal fixation constructs conventionally requires a surgeon to prepare a long incision aligned with the spinal column of a patient. The pedicle screws, hooks or other anchors are then inserted into a number of vertebrae after which the spine rod is located with respect to saddles or U-shaped channels attached to the pedicle screws. The spine rod is then bent to match the relative position of the pedicle screw heads. Visualization of the accuracy of the alignment of the spine rod and the screw heads may be difficult because of visual interference from tissue and blood in the surgical field. Conventional surgical methods require a large midline incision and retraction of skin, muscle and other tissue to provide the surgeon with sufficient visualization of the pedicle bone structure.
Bending of the spine rod is performed once the screws are placed into the vertebrae and, therefore, visualization of the accuracy of the placement and configuration of the spine rod is very difficult. Improper alignment and inaccurate bending of the spine rod decreases the effectiveness of the fixation construct and often increases the surgical difficulty and time required for the surgery. In combination with the relatively long incision required for the installation of the spine rod, extended surgical procedures and related difficulties or complications are generally recognized as major contributing influences for extended patient recovery and less than optimal spinal fixation results.